Keratoconjunctivitis sicca, also known as dry eye disease, or dysfunctional tear syndrome, is a multifunctional disorder of the tear film, and ocular surface which results in discomfort, visual disturbance, and often even in ocular surface damage. Its prevalence differs widely by regions and is estimated to range from about 7.4% in the USA to about 33% in Japan (J. L. Gayton, Clinical Ophthalmology 2009:3, 405-412). According to another estimate, approximately 3.2 million women and 1.05 million men suffer from keratoconjunctivitis sicca in the USA alone. If symptomatically mild cases are also considered, there could be as many as 20 million affected people in the USA.
The main physiological function of the tear film is the lubrication of the ocular surface and the inner eyelid. In addition, it supplies the ocular surface with the nutrients which it requires, provides a smooth and regular optical surface for the eye. Moreover, it protects the ocular surface against pathogens by various mechanisms, including mechanical removal of foreign particles but also through antimicrobial substances which it contains. Consequently, the loss in dynamic stability of the structure, composition, volume and distribution, as well as clearance of the tear film can lead to the development of dry eye disease.
The tear film is a dynamic structure composed of a mucous component, an aqueous component, and a lipid component. The innermost layer of the film is the mucous layer or component, which is bound to the ocular epithelium via the interaction of mucin molecules which are produced by conjunctival goblet cells and by stratified squameous cells of the conjunctiva and the cornea. The lubricating effect of the tear film is substantially based on the mucous layer and its composition.
On top of the mucous layer is the aqueous layer which is produced by the main and accessory lacrimal glands. Its primary function is to hydrate the mucous component and contribute to the transport of nutrients, electrolytes, antibacterial compounds, and oxygen to the ocular surface. The aqueous component contains water, electrolytes, lysozyme, lactoferrin, immunoglobulins (in particular IgA), retinol, hepatocyte growth factor, epidermal growth factor as its important constituents.
The outermost layer is the lipid layer, covering the aqueous layer. The lipid layer is formed from meibum (a complex mixture of polar and non-polar lipids including wax and cholesterol esters, phospholipids, di- and tri-glycerides and hydrocarbons) secreted by the meibomian (tarsal) glands which are positioned at the tarsal plates of the eyelids, and to some degree also by the glands of Zeis which open into the eyelash follicles. The lipid mixture, which has a low melting point and remains fluid at tissue and corneal temperature, is secreted into the marginal reservoirs of the upper and lower eyelid margins. It is understood that the blinking action helps to promote the spreading and mixing of the lipids in the lipid layer. The major role of the lipid layer is primarily to reduce the rate of evaporation of the aqueous layer by evaporation, but its functions also include enhancing the spreading of the tear film, forming a barrier to prevent tear film contamination, and providing a clear optical surface. It has been proposed that increased tear film stability is associated with a thicker tear film lipid layer.
It is today acknowledged that keratoconjunctivitis sicca is a complex, multifunctional disorder involving several interacting pathophysiological mechanisms which are only beginning to be understood (H. D. Perry, Am. J. Man. Care 13:3, S79-S87, 2008). The two mechanisms that are being discussed as pivotal in the etiology of this disease and which also appear to reinforce each other mutually are tear hyperosmolarity and tear film instability. Hyperosmolar tear fluid can result from excessive tear film evaporation or reduced aqueous flow. It activates an inflammatory cascade and causes the release of inflammatory mediators into the tear fluid, with multiple pathophysiological effects eventually leading to further increased tear film evaporation and tear film instability. Thus, tear film instability can be a consequence of hyperosmolarity. Alternatively, tear film instability can also develop through its own etiological pathway, for example via abnormalities of the lipid layer composition, such as from meibomian gland disease.
The inflammation cycle is one of the key processes that maintain and potentially progress the dry eye disease. Depending on the severity of the condition, patients often develop a reversible squameous metaphase and punctate erosions of the ocular epithelium. Secondary diseases whose development may be triggered by dry eye disease include filamentary keratitis, microbial keratitis, corneal neovascularisation, and ocular surface keratinisation.
Two major categories of dry eye disease (DED) are distinguished today, which are aqueous-deficient DED and evaporative DED. These conditions are not necessarily mutually exclusive.
Within the class of aqueous-deficient forms of DED, two major subtypes are differentiated, Sjögren and non-Sjögren. Sjögren syndrome patients suffer from autoimmune disorders in which the lacrimal glands are invaded by activated T-cells, which leads not only to keratoconjunctivitis sicca but also to a dry mouth condition. The Sjögren syndrome can be a primary disease or result from other autoimmune diseases such as systemic lupus erythrematosus or rheumathroid arthritis. Non-Sjögren patients suffering from an aqueous-deficient DED usually have a lacrimal gland insufficiency, lacrimal duct obstruction or reflex hyposecretion.
The second major class, evaporative DED, is also somewhat heterogeneous and can develop as a result of diverse root causes. Causes associated with increased evaporative loss of the tear film include meibomian gland disease, eyelid aperture disorders, blink disorders (as in Parkinson disease) or ocular surface disorders (as in allergic conjunctivitis). In particular, meibomian gland diseases are prevalently associated with evaporative dry eye disease. For example, meibomian gland dysfunction can result in changes in the quantitative or qualitative secretion of the lipid components required for the tear film. This in turn can lead to a failure in forming a stable and continuous tear film, which is followed by evaporative loss and hyperosmolarity. Meibomian gland dysfunction can often be characterized by gland obstruction and clogging through hyperkeratinisation of the gland and increased viscosity of the meibum. Dysfunction can arise from a primary lid-margin related disease or a secondary disease arising from systemic disorders such as acne rosacea or seborrheic dermatitis.
Among the many risk factors for dry eye disease that are known today, some of the best studied ones are advanced age and female sex. It appears that in particular postmenopausal women have a reduced tear production, probably related to hormonal effects which are not very well understood as yet. Further risk factors include diets with low omega-3-fatty acids, occupational factors (e.g. associated with reduced blink frequency), environmental conditions, contact lens wearing, ophthalmic surgery, certain systemic (anticholinergics, beta-blockers, isotretinoin, interferons, hormones) and ophthalmic medications (any frequently administered eye drops including artificial tears; especially formulations comprising preservatives), and a number of primary diseases such as Parkinson disease, hepatitis C, HIV infection, and diabetes mellitus.
The management of dry eye disease relies on both non-pharmacological and pharmacological approaches and the therapeutic options depend significantly on the severity of the disease state (M. A. Lemp, Am. J. Man. Care 14:3, S88-5101, 2008).
Pharmacological treatments are required for moderate to more severe forms of keratoconjunctivitis sicca. However, there are presently not many pharmacological therapies available which have proven to be effective and/or which have been authorized by the regulatory agencies. Treatment options with pharmaceutical active ingredients such as secretagogues (e.g. cholinergic agents such as muscarinic acetylcholine receptor antagonists) to stimulate tear production, and anti-inflammatory agents such as corticosteroids and oral tetracyclines have been proposed. In the US, the major pharmacological treatment for moderate to severe keratoconjunctivitis sicca is with ciclosporin (i.e. ciclosporin A, also known as cyclosporine A), which is an approved medicine in the form of an ophthalmic emulsions (Restasis®) for increasing “ . . . tear production in patients whose tear production is presumed to be suppressed due to ocular inflammation associated with keratoconjunctivitis sicca.” (Restasis prescribing information). In this case, according to the evidence that is available, topical ciclosporin is probably disease-modifying rather than only palliative.
Non-pharmacological approaches to treating dry eye disease and its symptoms are used initially when only mild symptoms occur, but also as palliative measures to support pharmacological and medical interventions. Non-pharmacological approaches may include the avoidance of exacerbating factors such as dry air, wind and drafts, tobacco smoke, modification of working habits; eye lid hygiene; tear supplementation; physical tear retention by punctal plugs or therapeutic contact lenses. In the case of dry eye disease exacerbated or caused by meibomian gland dysfunction, measures such as heat compresses, eye lid massaging or forced expression of the glands are also often recommended.
The mainstay of non-pharmacological DED treatment is the use of artificial tears for tear substitution. Most of the available products are designed as lubricants. In addition, they may function as carriers for nutrients and electrolytes (importantly, potassium and bicarbonate), and some products attempt to correct physical parameters such as an increased osmolarity in certain forms of DED. The major functional component of artificial tear compositions is an agent which increases or adjusts the viscosity, so as to increase retention time on the ocular surface and which at the same time also exhibits lubricant functionality. Common compounds used for this purpose include carboxymethylcellulose and its sodium salt (CMC, carmellose), polyvinyl alcohol, hydroxypropyl methylcellulose (HPMC, hypromellose), hyaluronic acid and its sodium salt, and hydroxypropyl guar gum. Hydrocolloids such as hydroxypropyl guar gum or hyaluronic acid exhibit some degree of bioadhesiveness and can act to add volume to the tear film. However, compositions with a relatively high viscosity, and in particular gel-type formulations, may have a tendency to cause visual blurring, as well as a tendency to cake and form residues on the eye margins and eyelashes.
Some artificial tears comprise lipids as substitutes for the lipid component, with the intention of mimicking the lipid layer of the natural tear film in order to decrease the rate of tear fluid evaporation. For example, U.S. Pat. No. 5,981,607 discloses compositions for the alleviation of symptoms related to dry eye based emulsions with higher fatty glycerides such as castor oil, corn oil or sunflower oil or light mineral oil. These types of lipids are, however physically and biochemically poorly related to native lipid compositions. Also, the exact fate of an emulsion mixed with tear fluid in a physiological setting is not completely predictable, especially in view of the variability in volume and content of the tear film in patients with dry eye disease.
In general, one of the disadvantages of such formulations comprising oil for ophthalmic administration is that these inherently may have a negative impact on vision. Whether used as oily solutions or oil-in-water emulsions, they exhibit a refractive index which differs substantially from that of physiological tear fluid, which leads to visual disturbances and blurring.
Also, in contrast to single phase systems, emulsions may be more complex and difficult to manufacture, especially in sterile form. Frequently, emulsions are not readily sterilisable by thermal treatment without negative impact on the physical properties of the emulsion. On the other hand, aseptic processing is complex, costly, and is associated with higher risks of failure, i.e. microbial contamination.
Oil-in-water emulsions are also more prone to microbial contamination during use as well. If they were to be presented in multi-dose containers which are in principle more cost-efficient and convenient for patients than single-use vials, they would have to be preserved in order to ensure their microbiological quality.
At the same time however, preservatives which can be used in ophthalmic formulations are potentially damaging to the eye, in particular to the ocular surface, and should be avoided in the context of dry eye disease. At least in earlier years, multi-dose formulations for ophthalmic administration had to be preserved using a physiologically acceptable preservative in order to reduce the risk of microbial contamination and infection. Most preservatives are however problematic for DED patients in that they have a potential to negatively affect the ocular surface, thus counteracting the therapeutic intent. This is particularly relevant for patients with moderate to severe dry eye disease symptoms who may require frequent use for symptom relief, as well as patients who require multiple preserved topical medicaments.
As an alternative, single-dose containers for the administration of non-preserved formulations were developed. These are however less cost-efficient and convenient to handle for the patient than the conventional multi-dose bottle. Furthermore, ophthalmic formulations utilizing ‘vanishing’ preservatives such as sodium chlorite or sodium perborate, which can convert to non-toxic ions and water after instillation and contact with the tear film, may still be irritating to patients especially those with severe disease who may not have sufficient tear volume to effectively degrade the preservatives.
WO 2011/073134 discloses ophthalmic topical pharmaceutical compositions comprising immunosuppressant macrolides such as ciclosporin A and semifluorinated alkanes, for treatment of keratoconjunctivitis sicca. The semifluorinated alkanes in the disclosed compositions serve as suitable liquid vehicles for delivering the therapeutic pharmaceutical agent to the eye, and in particular have a high capacity for dissolving extremely challenging poorly soluble compounds such as ciclosporin. However, no mention has been made as to the protective effect and spreading behaviour, in particular of synergistic semifluorinated alkane mixtures, on the tear film and the tear film lipid layer. Nor does the document discuss the solubilizing effect semifluorinated alkane mixtures may have for altered state meibum (such as the case in meibomian gland dysfunction, in which glands may be clogged).
U.S. Pat. No. 7,001,607 discloses a polyaphron gel tear substitute containing at least one water-soluble fluorinated surfactant, water, and a non-polar component, in which the nonpolar component can be fluorocarbon or a silicone oil. The gel compositions are specifically administered into the conjunctival sac to form a gel reservoir, and are only spread over the cornea of the eye as a liquid film over the cornea as a result of blinking action. For patients with dry eye symptoms caused by eyelid/blink disorders (e.g. as a result of Parkinson's disease), such compositions are therefore not useful. Moreover, as blinking is necessary to spread and liquefy the gel, it is likely that there would be significant visual blurring directly after instillation, which is also likely to be worse when incorrectly applied by the patient not directly into the conjunctival sac. Furthermore, the proposed fluorinated surfactants do not have an established clinical record of tolerability to the human eye, and they can have a damaging effect on the ocular surface (despite inclusion of non-polar components which may interact more strongly with them) once mixed with physiological tear fluid.
It is therefore an object of the present invention to provide a novel composition which is useful in the treatment of dry eye disease and symptoms and conditions associated therewith, and which at the same time addresses and overcomes the various issues and at least one of the limitations or disadvantages associated with prior art formulations. In a specific aspect, it is an object of the invention to provide a composition for the palliative treatment and care of the eye and eye tissue. In a further aspect, it is an object of the invention to provide a kit comprising a composition for the treatment of keratoconjunctivitis sicca which does not exhibit one or more of the disadvantages of prior art. Further objects of the invention will become clear on the basis of the following description, examples, and patent claims.